At Sea to Summit we have virtually eliminated the negative effects that moisture has on down with the introduction of water-repellent Ultra-Dry Down™. Ultra-Dry Down™ water-repellent treatment protects down from external moisture and internal condensation. Ultra-Dry Down™ is a permanent* Nano-level water repellent polymer treatment applied to our high loft, high quality down. The Nano-thin treatment vastly improves our down’s reaction to water without effecting its weight or loft performance. Ultra-Dry Down™ retains over 60% more loft and absorbs 30% less moisture when compared with untreated down. Sea to Summit sleeping bags dry out 60% faster than bags with untreated down. The Nano-level treatment also inhibits bacterial and microbial growth, which makes Sea to Summit sleeping bags more hygienic and improves their lifespan. Sea to Summit sleeping bags, using Ultra-Dry Down™ in combination with our already formidable 2D- and 3D-NanoShell™ system give you the best chance of sleeping warm and dry, day in day out throughout the worst of conditions. With these technologies combined there is simply no reason to choose any other insulation or shell for your sleeping bag.